ESD on outside CAT5

Maybe someone here can provide some insight on this.

A family member has a Motorola Canopy radio on a wood pole for fixed wireless Internet. It's about 20 feet up the pole. Direct bury CAT5 cable connects to it, goes down the pole, into the ground for about

100 feet to the house. Inside the house, the cable changes to interior CAT5 but goes straight to a computer.

The CAT5 has a copper shield on it, but it isn't connected to anything.

So far, two Ethernet cards have failed. In both cases, they failed during winter storms in which there was no lightning, but a lot of wind. They also get thunderstorms during the summer, but this hasn't caused any problems. The first time I thought a power outage caused it. Another outage failed the video card, so I suggested a UPS and they now have one.

However, when this last Ethernet card failed there were no power problems. I'm starting to think that maybe the wind is causing static buildup on the pole cable. How probable is that? How much would grounding the CAT5 shield help? It shouldn't hurt; I had intended on grounding it initially but for some reason didn't. I looked into Ethernet surge suppressors and that's an option, but I'd like to try and understand as much as possible about this problem first.

Even though the computer has integrated Ethernet, I installed an add- in card we had in case this happens again. I'd rather destroy a cheap NIC than something on the main board.

Reply to
hondgm
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There has to be an rj-45 isolator (lightning arrestor) out there somewhere.

Have you looked at the protection/protected jacks on a surge arresting power strip?

Maybe simply using one of those will do the job. At least look at how they 'isolate' the lines.

Reply to
Spurious Response

How does the radio operate with out power?

You should have the radio grounded at the pole. Ground the cable shield as well. And add a Cat5 lighting arrestor where it enters the house, with a ground rod as well.

Cheers

Reply to
Martin Riddle

c
p

and just as importantly, the shield of the cable should connect to the ground of the radio at the radio..

you want every conductor entering the radio to be at the same potential..

how does the radio get power?

Mark

Reply to
Mark

Cold wind => Static Charge build-up. ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

B&B electronics sells a decent Cat5 surge suppressor which works with PoE (just a so-far-happy customer). I prefer fiber for anything running network outside, but this seems like a place where that's not an option

- but the 100 feet of wire plus a pole is an invitation to trouble. Ground the shield as well.

--
Cats, coffee, chocolate...vices to live by
Reply to
Ecnerwal

Lots of good suggestions and information. Thanks to everyone.

As for the common question of how the radio gets power, there is a power injector in the house that I assume sends power through the normally unused 4 wires in 100BASE-TX. It's not real PoE, but their own inexpensive implementation.

Reply to
hondgm

"Artemus"

** The process is likely a bit more complicated.

The OP has foolishly left the foil shield connected to nothing - so it acquires the charge generated by wind or clouds. Up to 20kV is possible. There is significant capacitance between the shield and the signal carrying conductors - maybe 30 pF per foot. So with 120 feet, the total C is around

3.6nF. You work out the joules.

At some high voltage a discharge breakdown ( spark) will occur somewhere along the cable. This could be once in a while, every second or even a few times a second. It soon destroys semiconductors.

If the signal were TV or audio, you would see or hear the disturbances - but with data, the system plough right on till it stops.

..... Phil

Reply to
Phil Allison

Static buildup from the wind is possible. However it is more likely that the charge in the clouds is causing your problem. There can be a potential difference of 1 million volts, or more, between the ground and the bottom of a cloud. If the cloud bottom is 2000' AGL there is a voltage gradient of 500V per foot in the dielectric (air) between them. Your 20' pole could be seeing 10KV at the top. The impedance is very high so the currents will be very small but they can be sufficient to damage sensitive semiconductors. Ground everything as others have suggested. Art

Reply to
Artemus

Yes, wind builds up a nice charge in a set up like that..

Run a ground wire down the pole with a lightning rode and ground your shield at one end.

Jamie

Reply to
Jamie

You should have a surge suppresor on the line where it comes into the house. The Motorola p/n is SS600, a regular ethernet isolater/suppressor from someplace else may not work as Motoroa uses non-standard PoE. You'll need to use as shielded connector on the line from the pole.

Ground the suppressor where it comes into the house. If the line comes in near (

Reply to
Howard Eisenhauer

And a plain ol' lighting rod at the top of the pole could help dissipate the space charge.

Good Luck! Rich

Reply to
Rich Grise

Not the space between your ears!

Reply to
Chieftain of the Carpet Crawle

Its more than code. Any recommendations for a protector that does not connect short to single point ground is a bogus recommendation. No protector does protection. Not one. The earth ground is where energy must dissipate. Each structure must have its own single point earth ground. Every wire inside any cable that enters that structure must make a short connection to that single point ground.

An application note demonstrates that concept. Antenna and building both have their own single point ground. Even underground wires must be earthed short (ie 'less than 10 feet') to that earth ground:

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Every wire either connects directly to that earth ground. Or connects via a protector. No protector does protection. Either a protector connects surges to earth. Or that protector (ie one adjacent to the radio) may even make surge damage easier.

A direct lightning strike to one structure means a direct lightning strike to electronics in the other. Surges seek earth ground. If you did not earth every wire (as demonstrated), then the surge will use electronics in the other structure as a connection to earth.

Either a destructive transient makes a short (low impedance) connection to earth. Or that energy is inside hunting for earth destructively. Once inside, nothing will stop a destructive hunt. Ethernet cards have about

2000 volt protection. That damage is because a surge was all but invited to find earth via those interfaces. Protection always - as in no exceptions - always about energy dissipated outside a building. Protection is never about any protector. Protection is always about where that energy dissipates - single point earth ground.

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Reply to
westom

Little Tommy is back with his same cut & paste bullshit. Even the earth isn't at the same potential 100 feet apart during a lightning strike, but he's too ignorant to understand.

--
You can't fix stupid. You can't even put a Band-Aid? on it, because it's
Teflon coated.
Reply to
Michael A. Terrell

Firstly, there ought to be a ground at or near the mast (to protect the buried wire from high currents), and the radio has some kind of case that should be bonded to that ground (but not necessarily the CAT5 wiring). Then, before the CAT5 enters the house there should be a ground (maybe just to the outer shield) connection. And, if there's still a problem, interpose a cheap 5-port switch. It could be ANY PART of the computer that burns out next time, not necessarily just the card.

Reply to
whit3rd

For sure. I lost about 3 internal modems over a period of a few months in spring a few years ago and could not understand why. The telephone lines are buried, why am I not safe? Telephone guy told me: Sometimes lightning hits trees that are near to where the cable is buried. The lightning runs down the tree, through the roots which have grown to be near the cable, and enters the (insulated) cable.

I did not expect that. Live and learn.

John

Reply to
John - KD5YI

"John - KD5YI"

** So a "Telephone guy" told you that ??

Must be like hearing the word of god....

..... Phil

Reply to
Phil Allison

Do you have something better to offer? I'm always willing to learn.

John

Reply to
John - KD5YI

Makes no difference whether wires are buried or overhead. Phone lines already have a 'whole house' protector installed for free. That is not the traditional source of destructive surges (no matter how many times the uneducated Michael posts insults everywhere to mask his insecurities).

Protection means every wire in every incoming cable is earthed directly or via a 'whole house' protector. Once energy is inside a building, then nothing stops that destructive hunt for earth via appliances. Nothing. This is discussed extensively in ham radio groups.

Once energy is inside, it will hunt for earth. It will select appliances to damage. A most common source of surges that destroy modems is AC electric. A best path to earth is through than modem (most often via an off-hook relay), and to earth via the phone wire and 'whole house' protector.

Once energy is inside, then it will search for earth. If any wire enters a building without proper earthing, then nothing but protection already inside appliances (including a modem) will stop that hunt. Phone wires are rarely the incoming electrical path. And are a common outgoing path to earth once that energy has been permitted inside the building. Therefore every incoming wire (even underground) must connect to single point ground before entering.

Most likely reason for repeat modem damage is AC electric wires were not earthed at the service entrance.

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Reply to
westom

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